Silicone-modified single-component casting compound

ABSTRACT

A casting compound based on a resin which cures by a chemical reaction. The casting compound is suitable for insulation of electric components and contains an epoxy resin component, a silicone-containing component, a filler, and a thermal initiator. This casting compound is processible as a single-component system.

FIELD OF THE INVENTION

The present invention relates to a casting compound and a method ofproducing molded parts.

BACKGROUND INFORMATION

Casting compounds based on a resin which cures by a chemical reactionplay a major role in the production of industrial parts and components.They are used, among other things, for insulation purposes in electricand electronic components. Such casting compounds may be in the form oftwo-component systems, where one component is a hardener, which is mixedwith the other component containing reactive resins, fillers, etc. andthen is processed immediately. Preparation of the casting compound isintegrated into the processing operation and these compositions may notbe stored in a ready-to-use state at room temperature for three totwelve months, for example. That occupational safety in handling thecuring components may be ensured only at great technical complexitybecause the compounds used as the hardener are often hazardous to healthor irritants, e.g., carboxylic anhydrides or amines. Single-componentsystems have been developed for this reason.

German Published Patent Application No. 196 38 630 discusses suchcasting materials for underfilling electric and electronic componentswhich are used to protect against environmental influences and tostabilize solder connections on the components. Curing of thesingle-component systems discussed there is performed thermally and/orby exposure to UV radiation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a casting compoundwhich is stable in storage and is processible as a single-componentsystem, has a high thermal conductivity and cracking resistance,provides an electrical insulation effect, and is resistant to corrosivemedia such as fuels even at high temperatures.

The object of the present invention may be achieved according to thepresent invention by providing a casting compound which is processibleas a single-component system and contains a silicone-containingcomponent. This casting compound has a low viscosity and a goodcapillary action during processing, is characterized by a high thermalconductivity and cracking resistance, and adheres to a wide variety ofmaterials. In addition, it may withstand high thermal stresses and it isalso resistant at high temperatures to the influence of fuels.

The casting compound has a short curing time and a favorable reactionprofile and consequently is easily processible. This is accomplishedthrough the choice of a suitable initiator, which includes a cationiccrosslinking agent and a cocatalyst.

In an exemplary embodiment of the present invention, the castingcompound contains up to 90 wt % of a silicone-containing componentcontaining silicone elastomer particles as the silicone. This ensures ahigh mechanical load-bearing capacity in the cured state without anunwanted increase in the viscosity of the casting compound duringprocessing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows compounds I to VI, which are ring-epoxidized cycloaliphaticdiepoxies, for use in an epoxy resin component “A”.

DETAILED DESCRIPTION

Casting compounds according to the present invention include four basiccomponents, namely an epoxy resin component A, a silicone-containingcomponent B, a filler C, and an initiator D. In addition, othercomponents are also provided, these components generally being used inother casting compounds, e.g., foam suppressants, sedimentationinhibitors, and adhesive agents, the use of which is referred to inother systems.

In general, it should be noted that casting compounds form a stablesystem before and during processing to prevent separation of thecomponents. Thus, the filler particles should form a stable dispersionwith the epoxy resin components, and the epoxy resin components shouldin turn form stable emulsions with one another. This stability isensured during processing as well as in curing of a casting compound.

A variety of monomeric compounds having an epoxy function may be used asepoxy resin component A, either alone or in mixture with other compoundswith or without an epoxy function. However, diepoxies and/or triepoxiesmay be used; the commercially available compounds shown below are givenas examples:

Epoxy resin component A may include one or more of compounds (I) through(VI) as well as other components. Ring-epoxidized cycloaliphaticdiepoxies such as (I) and (VI) have proven to be especially suitable.Epoxy resin component A is present in the casting compound in the amountof 5 to 90 wt %, in particular 10 to 60 wt %.

Silicone-containing component B also contained in the casting compoundis a dispersion of one or more silicones in an epoxy resin. Suitablesilicones include both silicone block copolymers and silicone particles.The silicone particles may be silicone resin particles or siliconeelastomer particles, they may have a particle diameter of 10 nm to 100μm. The silicone particles may be used as core-shell particles includinga chemically modified surface, but it has been found that untreatedand/or surface-modified silicone particles, e.g., those treated withPMMA, are more suitable for the object of the present invention.Suitable epoxy resins may include all monomeric compounds having anepoxy function, used either alone or in mixtures with other compoundswith or without an epoxy function. However, the use of one or more ofthe diepoxies (I) through (VI) indicated above may be useful.Silicone-containing component B contains 10 to 80 wt % silicone, inparticular 40 wt %. The casting compound contains up to 90 wt % ofsilicone-containing component B.

The casting compound also contains one or more fillers C, a suitablechoice of which is capable of preventing shrinkage of the castingcompound during processing and makes the thermal conductivity of thecasting compound in the cured state adjustable. Thus, for example,quartz powder, aluminum oxide, chalk, fused silica or talc, optionallyin mixture with silicon carbide are suitable as filler C. The use ofsilanized quartz powder has proven especially suitable, where thesilanization may be performed either in situ by adding a silane or inadvance by silanizing the quartz powder. Filler C is present in thecasting compound in the amount of 5 to 75 wt %, in particular 40 to 60wt %.

As fourth component D, the casting compound contains an initiator whichpermits a sufficiently rapid reaction at an elevated temperature.Suitable initiators include both thermal initiators and photoinitiators.

To ensure that the casting compound will be processible as asingle-component system, a cationic crosslinking agent was selected asthe initiator. It may be, for example, a quinolinium, sulfonium,iodonium, or boroiodonium compound. These result in cationicpolymerization of the epoxy resin.

The initiator may also contain a cocatalyst which functions inparticular to lower the starting temperature of the reaction. It may bean agent such as benzopinacol which forms free radicals. The choice ofinitiator determines the course of the reaction in curing. Thecombination of a cationic crosslinking agent with a cocatalyst resultsin a suitable reaction rate profile characterized by an optimum,narrowly defined reaction temperature at which the reaction proceedspromptly, without a slow reaction starting at even lower temperaturessuch as room temperature. This is also a prerequisite for a good shelflife of the single-component system at room temperature.

The casting compound is processed at an elevated temperature to yield amolded article. The casting compound has such a low viscosity and such ahigh capillary action with appropriate heating that it is suitable forcasting even difficult geometric shapes such as casting gaps having adiameter of <200 μm. At the same time, this permits very short cycletimes. The casting compound after casting is exposed to a temperature of60° C. to 110° C. for 30 to 300 minutes or 120° C. for 10 to 100 minutesto induce gelation of the casting compound. Then it is exposed to atemperature of 140° C. to 220° C. for 10 to 90 minutes to cure themolded article. The processing time is thus significantly less than 50%of the time normally required for casting a two-component composition.

The method steps of gelation and curing may be combined in a single stepby exposing the casting compound to a temperature of 140° C. to 220° C.immediately after casting.

Exemplary embodiments of casting compounds and/or their formulations andthe resulting properties in the cured state are presented below asexamples.

Compositions:

Example 1 2 3 4 Epoxy resin 88 75 62 52 component A Silicone-containing12 25 38 48 component B Filler C 100 100 100 100 Silicone-containing0.075 0.075 0.075 0.075 foam suppressant Sedimentation 0.2 0.2 0.2 0.2inhibitor

These compositions are given in parts by weight, the initiator beingadded in very low concentrations of 0.1 to 5 wt % in each case. Thecompositions indicated above yield the following profile of properties:

viscosity at 60° C. 100 to 1000 mPas After curing: linear shrinkage: 0.4 to 0.7% glass transition temperature: 150 to 165° C. thermalexpansion coefficient:  30 to 50 * 10⁻⁶ 1/° C. double K_(1c)  0.8 to1.15 MPa√m torsion test: G_(1c) 100 to 236 J/m² thermal conductivity: 0.5 to 0.7 W/m * K weight change in diesel fuel  0 to 1.7% after 300hours at 200° C.: change in volume in diesel fuel  0 to 3.7% after 300hours at 200° C.: change in flexural strength in  7.5 to 26% diesel fuelafter 300 hours at 200° C.: change in selvedge thread  7.5 to 35%elongation in diesel fuel after 300 hours at 200° C.:

The casting compound is suitable, e.g., for electrical insulation andmechanical fixation and to protect electric windings of electromagneticactuators from corrosive media. Such actuators may be integrated intosolenoid valves, for example, specifically in diesel or gasolinesolenoid valves.

The present invention is not limited to the exemplary embodimentsdescribed here, but instead others are also conceivable in addition tothe fields of application described here, e.g., use of the castingcompound in the manufacture of sensors, in particular for the enginecompartment of motor vehicles, and transmissions and fuel tanks, inparticular for motor vehicles.

1. A casting compound based on a resin which cures by a chemicalreaction for use in an insulation of an electric component, the castingcompound comprising: an epoxy resin component; a silicone-containingcomponent; a filler; and an initiator which includes a co-catalyst;wherein the casting compound is processible as a single-componentsystem; wherein the filler is a talc; wherein the epoxy resin componentincludes an epoxy resin based on a cycloaliphatic diepoxy; wherein theinitiator includes a cationic crosslinking agent; wherein the cationiccrosslinking agent includes a boroiodonium compound; and wherein theinitiator defines a reaction rate profile characterized by a narrowlydefined reaction temperature, the narrowly defined reaction temperaturebeing above room temperature such that the casting compound is stable atroom temperature.
 2. The casting compound of claim 1, wherein the epoxyresin component is present in an amount of 5 to 90 wt %.
 3. The castingcompound of claim 1, wherein the silicone-containing component includesa dispersion of a silicone in an epoxy resin based on a diepoxy.
 4. Thecasting compound of claim 1, wherein the silicone-containing componentis present in an amount of up to 90 wt %.
 5. The casting compound ofclaim 3, wherein the silicone-containing component includes 10 to 80 wt% of a silicone.
 6. The casting compound of claim 4, wherein thesilicone-containing component includes 10 to 80 wt % of a silicone. 7.The casting compound of claim 3, wherein the silicone-containingcomponent includes silicone elastomer particles as the silicone.
 8. Thecasting compound of claim 7, wherein the silicone elastomer particleshave a particle diameter of 10 nm to 100 μm.
 9. The casting compound ofclaim 1, wherein the filler includes at least one of a powdered quartzand an aluminum oxide.
 10. The casting compound of claim 1, wherein thefiller is present in an amount of 5 to 75 wt %
 11. The casting compoundof claim 1, wherein the filler is present in the amount of 40 to 60 wt%.
 12. The casting compound of claim 1, wherein the co-catalyst includesa radical former.
 13. The casting compound of claim 1, wherein theco-catalyst includes a benzopinacol.
 14. The casting compound of claim1, wherein the casting compound is free of anhydride.
 15. The castingcompound of claim 1, wherein the casting compound is used to manufacturean electromagnetic actuator.
 16. The casting compound of claim 1,wherein the casting compound is used to manufacture at least one of asolenoid valve, a diesel solenoid valve and a gasoline solenoid valve.17. The casting compound of claim 1, wherein the casting compound isused to manufacture a sensor for an engine compartment of a motorvehicle.
 18. The casting compound of claim 1, wherein the castingcompound is used to manufacture a transmission for a motor vehicle. 19.The casting compound of claim 1, wherein the casting compound is used tomanufacture a fuel tank for a motor vehicle.
 20. The casting compound ofclaim 1, wherein the filler includes a quartz powder.
 21. The castingcompound of claim 1, wherein the initiator is added in an amount of 0.1to 5 wt %.
 22. A casting compound based on a resin which cures by achemical reaction for use in an insulation of an electric component, thecasting compound comprising: an epoxy resin component; asilicone-containing component; a filler; and an initiator which includesa co-catalyst; wherein the casting compound is processible as asingle-component system; wherein the filler is a talc; wherein theinitiator includes a cationic crosslinking agent; wherein the cationiccrosslinking agent includes a boroiodonium compound; and wherein theinitiator defines a reaction rate profile characterized by a narrowlydefined reaction temperature, the narrowly defined reaction temperaturebeing above room temperature such that the casting compound is stable atroom temperature.
 23. A method for manufacturing a molded part for usein insulating an electric component, the method comprising: introducinga casting compound as a single-component system into a casting mold;exposing the casting compound to a first elevated temperature to form agel; and exposing the casting compound to a second elevated temperatureto cure the molded part; wherein the casting compound includes: an epoxyresin component; a silicone-containing component; a filler; and aninitiator which includes a co-catalyst; wherein the filler is a talc;wherein the epoxy resin component includes an epoxy resin based on acycloaliphatic diepoxy; wherein the initiator includes a cationiccrosslinking agent; wherein the cationic crosslinking agent includes aboroiodonium compound: and wherein the initiator defines a reaction rateprofile characterized by a narrowly defined reaction temperature, thenarrowly defined reaction temperature being above room temperature suchthat the casting compound is stable at room temperature.
 24. A methodfor manufacturing a molded part for use in insulating an electriccomponent, the method comprising: introducing a casting compound as asingle-component system into a casting mold; exposing the castingcompound to a first elevated temperature to form a gel; and exposing thecasting compound to a second elevated temperature to cure the moldedpart; wherein the casting compound includes: an epoxy resin component; asilicone-containing component; a filler; and an initiator which includesa co-catalyst; wherein the first elevated temperature is one of 60 to110° C. for 30 to 300 minutes and 100 to 140° C. for 10 to 100 minutes;wherein the filler is a talc; wherein the initiator includes a cationiccrosslinking agent; wherein the cationic crosslinking agent includes aboroiodonium compound; and wherein the initiator defines a reaction rateprofile characterized by a narrowly defined reaction temperature, thenarrowly defined reaction temperature being above room temperature suchthat the casting compound is stable at room temperature.
 25. A methodfor manufacturing a molded part for use in insulating an electriccomponent, the method comprising: introducing a casting compound as asingle-component system into a casting mold; exposing the castingcompound to a first elevated temperature to form a gel; and exposing thecasting compound to a second elevated temperature to cure the moldedpart; wherein the casting compound includes: an epoxy resin component; asilicone-containing component; a filler; and an initiator which includesa co-catalyst; wherein the second elevated temperature is 140 to 220° C.for 10 to 90 minutes; wherein the filler is a talc; wherein the epoxyresin component includes an epoxy resin based on a cycloaliphaticdiepoxy; wherein the initiator includes a cationic crosslinking agent;wherein the cationic crosslinking agent includes a boroiodoniumcompound; and wherein the initiator defines a reaction rate profilecharacterized by a narrowly defined reaction temperature, the narrowlydefined reaction temperature being above room temperature such that thecasting compound is stable at room temperature.